This project studies several types of instrumentation to understand basic aspects of their operation as required for optimizing their operation. Dr. George Weiss has been working with Drs. Sinisa Pajevic, Marian Bogunya (CIT) and Dr. Peter Basser (NICHD) on determining statistical properties of tract following by Diffusion Tensor Imaging, in particular studying how far, on average it is possible to follow a fiber by this method before it is completely corrupted by random noise. We showed that in the ideal case of a straight fiber one could formulate the problem in terms of a diffusion model with an extrapolated absorbing boundary. The results of analyzing this model was in excellent agreement with simulated data. A paper containing these results has been submitted to Magnetic Resonance in Medicine. A second project concerns the use of single-molecule spectroscopy (SMS) techniques to measure rate constants in chemical reactions. A variety of problems in this area have been explored together with Drs. Marian Bogunya, Alexander Berezhkovskii, and Attila Szabo (NIDDK). An earlier result derived by us gave an exact mathematical solution for calculating rate constants for the ideal isomerization reaction. Further formalism has been developed for analyzing more complicated reactions. We have just begun to study the question of how precise these measurements are.